Ligand Steric Profile Tunes the Reactivity of Indium Phosphide Clusters.

Indium phosphide quantum dots have become an industrially relevant material for solid-state lighting and wide color gamut displays. The synthesis of indium phosphide quantum dots from indium carboxylates and tris(trimethylsilyl)phosphine (P(SiMe3)3) is understood to proceed through the formation of magic-sized clusters, with In37P20(O2CR)51 being the key isolable intermediate. The reactivity of the In37P20(O2CR)51 cluster is a vital parameter in controlling the conversion to quantum dots. Herein, we report structural perturbations of In37P20(O2CR)51 clusters induced by tuning the steric properties of a series of substituted phenylacetate ligands. This approach allows for control over reactivity with P(SiMe3)3, where meta-substituents enhance the susceptibility to ligand displacement, and para-substituents hinder phosphine diffusion to the core. Thermolysis studies show that with complete cluster dissolution, steric profile can modulate the nucleation period, resulting in a nanocrystal size dependence on ligand steric profile. The enhanced stability from ligand engineering also allows for the isolation and structural characterization by single-crystal X-ray diffraction of a new III-V magic-sized cluster with the formula In26P13(O2CR)39. This intermediate precedes the In37P20(O2CR)51 cluster on the InP QD reaction coordinate. The physical and electronic structure of this cluster are analyzed, providing new insight into previously unrecognized relationships between II-VI and III-V materials and the discrete growth of III-V cluster intermediates.

Regioselective Fluorohydrin Synthesis from Allylsilanes and Evidence for a Silicon-Fluorine Gauche Effect.

Allylsilanes can be regioselectively transformed into the corresponding 3-silylfluorohydrin in good yield using a sequence of epoxidation followed by treatment with HF·Et3N with or without isolation of the intermediate epoxide. Various silicon-substitutions are tolerated, resulting in a range of 2-fluoro-3-silylpropan-1-ol products from this method. Whereas other fluorohydrin syntheses by epoxide opening using HF·Et3N generally require more forcing conditions (e.g., higher reaction temperature), opening of allylsilane-derived epoxides with this reagent occurs at room temperature. We attribute this rate acceleration along with the observed regioselectivity to a ß-silyl effect that stabilizes a proposed cationic intermediate. The use of enantioenriched epoxides indicates that both SN1- and SN2-type mechanisms may be operable depending on substitution at silicon. Conformational analysis by NMR and theory along with a crystal structure obtained by X-ray diffraction points to a preference for silicon and fluorine to be proximal to one another in the products, perhaps favored due to electrostatic interactions.

Correlation of Local Isomerization Induced Lateral and Terminal Torsions with Performance and Stability of Organic Photovoltaics.

Organic photovoltaics (OPVs) have achieved great progress in recent years due to delicately designed non-fullerene acceptors (NFAs). Compared with tailoring of the aromatic heterocycles on the NFA backbone, the incorporation of conjugated side-groups is a cost-effective way to improve the photoelectrical properties of NFAs. However, the modifications of side-groups also need to consider their effects on device stability since the molecular planarity changes induced by side-groups are related to the NFA aggregation and the evolution of the blend morphology under stresses. Herein, a new class of NFAs with local-isomerized conjugated side-groups are developed and the impact of local isomerization on their geometries and device performance/stability are systematically investigated. The device based on one of the isomers with balanced side- and terminal-group torsion angles can deliver an impressive power conversion efficiency (PCE) of 18.5%, with a low energy loss (0.528 V) and an excellent photo- and thermal stability. A similar approach can also be applied to another polymer donor to achieve an even higher PCE of 18.8%, which is among the highest efficiencies obtained for binary OPVs. This work demonstrates the effectiveness of applying local isomerization to fine-tune the side-group steric effect and non-covalent interactions between side-group and backbone, therefore improving both photovoltaic performance and stability of fused ring NFA-based OPVs.

LVVO-Ethyl Maltol-Based Metallodrugs (L2- = Tridentate ONO Ligands): Hydrophobicity, Hydrolytic Stability, and Cytotoxicity via ROS-Mediated Apoptosis.

Four new oxidovanadium [VVOL1-4(ema)] complexes (1-4) have been synthesized using tridentate binegative ONO donor ligands H2L1-4 [H2L1: (E)-N'-(2-hydroxybenzylidene)furan-2-carbohydrazide; H2L2: (E)-N'-(4-(diethylamino)-2-hydroxybenzylidene)thiophene-2-carbohydrazide; H2L3: (E)-2-(4-(diethylamino)-2-hydroxybenzylideneamino)-4-methylphenol; H2L4: (E)-2-(3-ethoxy-2-hydroxybenzylideneamino)-4-methylphenol] and ethyl maltol (Hema) as a bidentate uninegative coligand and characterized by CHNS analysis, IR, UV-vis, NMR, and HR-ESI-MS methods. The structures of 1, 3, and 4 are confirmed by single-crystal X-ray analysis. The hydrophobicity and hydrolytic stability of the complexes are tested using NMR and HR-ESI-MS and correlated with their observed biological activities. It is observed that 1 hydrolyzed into a penta-coordinated vanadium-hydroxyl species (VVOL1-OH) with the release of ethyl maltol, whereas 2-4 are found quite stable under the investigated time period. The biomolecular interaction of 1-4 with DNA and BSA was performed using absorbance, fluorescence, and circular dichroism techniques. The in vitro cytotoxicity activities of H2L1-4 and 1-4 were tested against A549, HT-29, and NIH-3T3 cell lines. Among complexes, 2 with an IC50 value of 4.4 ± 0.1 µM displayed maximum anticancer activity against the HT-29 cell line. Complexes induce cell cycle arrest at the G2/M phase and subsequently trigger dose-dependent cell apoptosis, which is obtained by the cell apoptosis analysis via flow cytometry and confocal microscopy assays. Being fluorescence active, 1-4 were observed to target the mitochondria and exhibit disruption of the mitochondrial membrane potential, which consequently causes overproduction of intracellular reactive oxygen species and induced cell apoptosis.

Probing Edge/Support Electronic Cooperativity in Single Edge Fe/Co6Se8 Clusters.

This study provides insights into the electronic structure of an atomically precise Fe/Co6Se8 cluster and the extent of redox cooperativity between the Fe active site and the noninnocent Co6Se8 support. Chemical oxidation studies enable the isolation of two types of oxidized Fe/Co6Se8 clusters, in which the nature of the counterion (I- or OTf-) significantly impacts the structural interactions between Fe and the Co6Se8 unit. Experimental characterization by single crystal X-ray diffraction, 57Fe Mössbauer spectroscopy, and 31P{1H} NMR spectroscopy is complemented by computational analysis. In aggregate, the study reveals that upon oxidation, the charge is shared between the Fe edge site and the Co6Se8 core.

Correlation of Broad Absorption Band with Small Singlet-Triplet Energy Gap in Organic Photovoltaics.

Organic photovoltaics (OPV) are one of the most effective ways to harvest renewable solar energy, with the power conversion efficiency (PCE) of the devices soaring above 19 % when processed with halogenated solvents. The superior photocurrent of OPV over other emerging photovoltaics offers more opportunities to further improve the efficiency. Tailoring the absorption band of photoactive materials is an effective way to further enhance OPV photocurrent. However, the field has mostly been focusing on improving the near-infrared region photo-response, with the absorption shoulders in short-wavelength region (SWR) usually being neglected. Herein, by developing a series of non-fullerene acceptors (NFAs) with varied side-group conjugations, we observe an enhanced SWR absorption band with increased side-group conjugation length. The underpinning factors of how molecular structures and geometries improve SWR absorption are clearly elucidated through theoretical modelling and crystallography. Moreover, a clear relationship between the enhanced SWR absorption and reduced singlet-triplet energy gap is established, both of which are favorable for the OPV performance and can be tailored by rational structure design of NFAs. Finally, the rationally designed NFA, BO-TTBr, affords a decent PCE of 18.5 % when processed with a non-halogenated green solvent.

Multi-active Site Dynamics on a Molecular Cr/Co/Se Cluster Catalyst.

This study uncovers the interconnected reactivity of the three catalytically active sites of an atomically precise nanocluster Cr3(py)3Co6Se8L6 (1(py)3, L = Ph2PNTol-, Ph = phenyl, Tol = 4-tolyl). Catalytic and stoichiometric studies into tosyl azide activation and carbodiimide formation enabled the isolation and crystallographic characterization of key catalytically competent metal-imido intermediates, including the tris(imido) cluster 1(NTs)3, the catalytic resting state 1(NTs)3(CNtBu)3, and the site-differentiated mono(imido) cluster 1(NTs)(CNtBu)2. In the stoichiometric regime, nitrene transfer proceeds via a stepwise mechanism, with the three active sites engaging sequentially to produce carbodiimide. Moreover, the chemical state of neighboring active sites was found to regulate the affinity for substrates of an individual Cr-imido edge site, as revealed by comparative structural analysis and CNtBu binding studies.

Metal-Support Interactions in Molecular Single-Site Cluster Catalysts.

This study provides atomistic insights into the interface between a single-site catalyst and a transition metal chalcogenide support and reveals that peak catalytic activity occurs when edge/support redox cooperativity is maximized. A molecular platform MCo6Se8(PEt3)4(L)2 (1-M, M = Cr, Mn, Fe, Co, Cu, and Zn) was designed in which the active site (M)/support (Co6Se8) interactions are interrogated by systematically probing the electronic and structural changes that occur as the identity of the metal varies. All 3d transition metal 1-M clusters display remarkable catalytic activity for coupling tosyl azide and tert-butyl isocyanide, with Mn and Co derivatives showing the fastest turnover in the series. Structural, electronic, and magnetic characterization of the clusters was performed using single crystal X-ray diffraction, 1H and 31P nuclear magnetic resonance spectroscopy, electronic absorption spectroscopy, cyclic voltammetry, and computational methods. Distinct metal/support redox regimes can be accessed in 1-M based on the energy of the edge metal's frontier orbitals with respect to those of the cluster support. As the degree of electronic interaction between the edge and the support increases, a cooperative regime is reached wherein the support can deliver electrons to the catalytic site, increasing the reactivity of key metal-nitrenoid intermediates.

A Cyclic Ruthenium Benzylidene Initiator Platform Enhances Reactivity for Ring-Expansion Metathesis Polymerization.

Ring-expansion metathesis polymerization (REMP) has shown potential as an efficient strategy to access cyclic macromolecules. Current approaches that utilize cyclic olefin feedstocks suffer from poor functional group tolerance, low initiator stability, and slow reaction kinetics. Improvements to current initiators will address these issues in order to develop more versatile and user-friendly technologies. Herein, we report a reinvigorated tethered ruthenium-benzylidene initiator, CB6, that utilizes design features from ubiquitous Grubbs-type initiators that are regularly applied in linear polymerizations. We report the controlled synthesis of functionalized cyclic poly(norbornene)s and demonstrate that judicious ligand modifications not only greatly improve kinetics but also lead to enhanced initiator stability. Overall, CB6 is an adaptable platform for the study and application of cyclic macromolecules via REMP.

Tuning the Electronic Structure of Atomically Precise Sn/Co/Se Nanoclusters via Redox Matching of Tin(IV) Surface Sites.

A new strategy is reported to tailor the electronic properties of a superatomic metal chalcogenide cluster by redox matching the cluster core with surface tin(IV) sites. Two ternary clusters (SnR2)3Co6Se8L6 (R = Me, nBu) are synthesized by salt metathesis from the hexalithiated salt [Li2(py)2]3Co6Se8L6 and R2SnCl2. Cyclic and differential-pulse voltammetry studies reveal that the tristannylated clusters feature two new, near-degenerate, electronic states within the highest occupied molecular orbital-lowest unoccupied molecular orbital gap of the Co6Se8 core, which are attributed to the reduction of a surface tin site. Single-crystal X-ray diffraction analysis reveals that no Sn···Se coordination is present in the solid state. The single-crystal X-ray structure of the hexalithiated salt starting material is reported for the tetrahydrofuran (THF) adduct variant [Li2(THF)2]6Co6Se8L6.

CO2 Hydrogenation Catalyzed by a Ruthenium Protic N-Heterocyclic Carbene Complex.

We describe the hydrogenation of CO2 to formate catalyzed by a Ru(II) bis(protic N-heterocyclic carbene, p-NHC) phosphine complex [Ru(bpy)(MeCN)(PPh(p-NHC)2)](PF6)2 (1). Under catalytic conditions (20 µmol catalyst, 20 bar CO2, 60 bar H2, 5 mL THF, 140 °C, 16 h), the activity of 1 is limited only by the amount of K3PO4 present in the reaction, yielding a nearly 1:1 ratio of turnover number (TON) to equivalents of K3PO4 (relative to 1), with the highest TON = 8040. Additionally, analysis of the reaction solution post-run reveals the catalyst intact with no free ligand observed. Stoichiometric studies, including examination of unique carbamate and hydride complexes as relevant intermediates, were carried out to probe the operative mechanism and understand the importance of metal-ligand cooperativity in this system.

Robust Synthetic Route toward Anisotropic Metal-Organic Cages with Tunable Surface Chemistry.

Metal-organic cages with well-defined interior cavities and tunable surface chemistry serve as attractive building blocks for new types of soft nanoporous materials. While a compositionally diverse repertoire of metal-organic cages exists, the vast majority feature highly symmetric cores. Here, we report a robust, generalizable synthetic route toward anisotropic copper paddlewheel-based cages with tunable pendant amide groups. An isostructural family with increasingly hydrophobic surface properties has been synthesized and characterized by single-crystal X-ray diffraction, gas sorption analysis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and 1H NMR digestion experiments. The metal-organic cages reported here may enable a deeper study of how anisotropy influences the long-range structure and emergent function of soft nanoporous materials.

Structural, Electronic and Thermochemical preference for multi-PCET reactivity of Ruthenium(II)-Amine and Ruthenium(IV)-Amido Complexes.

The multiredox reactivity of bioinorganic cofactors is often coupled to proton transfers. Here we investigate the structural, thermochemical, and electronic structure of ruthenium-amino/amido complexes with multi- proton-coupled electron transfer reactivity. The bis(amino)ruthenium(II) and bis(amido)ruthenium(IV) complexes [RuII(bpy)(en*)2]2+ (RuII-H0 ) and [RuIV(bpy)(en*-H2)2]2+ (RuIV-H2 ) interconvert reversibly with the transfer of 2e-/2H+ (bpy = 2,2'-bipyridine, en* = 2,3-diamino-2,3-dimethylbutane). X-ray structures allow correlations between the structural and electronic parameters, and the thermochemical data of the 2e-/2H+ multi-square grid scheme. Redox potentials, acidity constants and DFT calculations reveal potential intermediates implicated in 2e-/2H+ reactivity with organic reagents in non-protic solvents, which shows a strong inverted redox potential favouring 2e-/2H+ transfer. This is suggested to be an attractive system for potential one-step (concerted) transfer of 2e-and 2H+ due to the small changes of the pseudo-octahedral geometries and the absence of charge change, indicating a relatively small overall reorganization energy.

Increasing reactivity by incorporating π-acceptor ligands into coordinatively unsaturated thiolate-ligated iron(II) complexes.

Reported herein is the structural, spectroscopic, redox, and reactivity properties of a series of iron complexes containing both a π-donating thiolate, and π-accepting N-heterocycles in the coordination sphere, in which we systematically vary the substituents on the N-heterocycle, the size of the N-heterocycle, and the linker between the imine nitrogen and tertiary amine nitrogen. In contrast to our primary amine/thiolate-ligated Fe(II) complex, [FeII(SMe2N4(tren))]+ (1), the Fe(II) complexes reported herein are intensely colored, allowing us to visually monitor reactivity. Ferrous complexes with R = H substituents in the 6-position of the pyridines, [FeII(SMe2N4(6-H-DPPN)]+ (6) and [FeII(SMe2N4(6-H-DPEN))(MeOH)]+ (8-MeOH) are shown to readily bind neutral ligands, and all of the Fe(II) complexes are shown to bind anionic ligands regardless of steric congestion. This reactivity is in contrast to 1 and is attributed to an increased metal ion Lewis acidity assessed via aniodic redox potentials, Ep,a, caused by the π-acid ligands. Thermodynamic parameters (ΔH, ΔS) for neutral ligand binding were obtained from T-dependent equilibrium constants. All but the most sterically congested complex, [FeII(SMe2N4(6-Me-DPPN)]+ (5), react with O2. In contrast to our Mn(II)-analogues, dioxygen intermediates are not observed. Rates of formation of the final mono oxo-bridged products were assessed via kinetics and shown to be inversely dependent on redox potentials, Ep,a, consistent with a mechanism involving electron transfer.

A Non-fullerene Acceptor with Enhanced Intermolecular π-Core Interaction for High-Performance Organic Solar Cells.

Understanding the molecular structure and self-assembly of thiadiazole-derived non-fullerene acceptors (NFAs) is very critical for elucidating the origin of their extraordinary charge generation and transport properties that enable high power conversion efficiencies to be achieved in these systems. A comprehensive crystallographic study on a state-of-the-art NFA, Y6, and its selenium analog, CH1007, has been conducted which revealed that the face-to-face π-core interaction induced by benzo[2,1,3]thiadiazole S-N-containing moieties plays a significant role in governing the molecular geometries and unique packing of Y6 and CH1007 to ensure their superior charge-transport properties. Moreover, benefitting from the red-shifted optical absorption via selenium substitution, photovoltaic devices based on a PM6:CH1007:PC71BM ternary blend delivered an exceptionally high short-circuit current of 27.48 mA/cm2 and a power conversion efficiency of 17.08%.

Diversion of Catalytic C-N Bond Formation to Catalytic Oxidation of NH3 through Modification of the Hydrogen Atom Abstractor.

We report that (TMP)Ru(NH3)2 (TMP = tetramesitylporphryin) is a molecular catalyst for oxidation of ammonia to dinitrogen. An aryloxy radical, tri-tert-butylphenoxyl (ArO·), abstracts H atoms from a bound ammonia ligand of (TMP)Ru(NH3)2, leading to the discovery of a new catalytic C-N coupling to the para position of ArO· to form 4-amino-2,4,6-tri-tert-butylcyclohexa-2,5-dien-1-one. Modification of the aryloxy radical to 2,6-di-tert-butyl-4-tritylphenoxyl radical, which contains a trityl group at the para position, prevents C-N coupling and diverts the reaction to catalytic oxidation of NH3 to give N2. We achieved 125 ± 5 turnovers at 22 °C for oxidation of NH3, the highest turnover number (TON) reported to date for a molecular catalyst.

Probing CO Generation through Metal-Assisted Alcohol Dehydrogenation in Metal-2-(arylazo)phenol Complexes Using Isotopic Labeling (Metal = Ru, Ir): Synthesis, Characterization, and Cytotoxicity Studies.

The reaction of 2-{2-(benzo[1,3]dioxol-5-yl)- diazo}-4-methylphenol (HL) with [Ru(PPh3)3Cl2] in ethanol resulted in the carbonylated ruthenium complex [RuL(PPh3)2(CO)] (1), wherein metal-assisted decarbonylation via in situ ethanol dehydrogenation is observed. When the reaction was performed in acetonitrile, however, the complex [RuL(PPh3)2(CH3CN)] (2) was obtained as the main product, probably by trapping of a common intermediate through coordination of CH3CN to the Ru(II) center. The analogous reaction of HL with [Ir(PPh3)3Cl] in ethanol did not result in ethanol decarbonylation and instead gave the organoiridium hydride complex [IrL(PPh3)2(H)] (3). Unambiguous evidence for the generation of CO via ruthenium-assisted ethanol oxidation is provided by the synthesis of the 13C-labeled complex, [Ru(PPh3)2L(13CO)] (1A) using isotopically labeled ethanol, CH313CH2OH. To summarize all the evidence, a ruthenium-assisted mechanistic pathway for the decarbonylation and generation of alkane via alcohol dehydrogenation is proposed. In addition, the in vitro antiproliferative activity of complexes 1-3 was tested against human cervical (HeLa) and human colorectal adenocarcinoma (HT-29) cell lines. Complexes 1-3 showed impressive cytotoxicity against both HeLa (half-maximal inhibitory concentration (IC50) value of 3.84-4.22 µM) and HT-29 cancer cells (IC50 values between 3.3 and 4.5 µM). Moreover, the complexes were comparatively less toxic to noncancerous NIH-3T3 cells.

New VIV, VIVO, VVO, and VVO2 Systems: Exploring their Interconversion in Solution, Protein Interactions, and Cytotoxicity.

The synthesis and characterization of one oxidoethoxidovanadium(V) [VVO(L1)(OEt)] (1) and two nonoxidovanadium(IV) complexes, [VIV(L2-3)2] (2 and 3), with aroylhydrazone ligands incorporating naphthalene moieties, are reported. The synthesized oxido and nonoxido vanadium complexes are characterized by various physicochemical techniques, and their molecular structures are solved by single crystal X-ray diffraction (SC-XRD). This revealed that in 1 the geometry around the vanadium atom corresponds to a distorted square pyramid, with a O4N coordination sphere, whereas that of the two nonoxido VIV complexes 2 and 3 corresponds to a distorted trigonal prismatic arrangement with a O4N2 coordination sphere around each "bare" vanadium center. In aqueous solution, the VVO moiety of 1 undergoes a change to VVO2 species, yielding [VVO2(L1)]- (1'), while the nonoxido VIV-compounds 2 and 3 are partly converted into their corresponding VIVO complexes, [VIVO(L2-3)(H2O)] (2' and 3'). Interaction of these VVO2, VIVO, and VIV systems with two model proteins, ubiquitin (Ub) and lysozyme (Lyz), is investigated through docking approaches, which suggest the potential binding sites: the interaction is covalent for species 2' and 3', with the binding to Glu16, Glu18, and Asp21 for Ub, and His15 for Lyz, and it is noncovalent for species 1', 2, and 3, with the surface residues of the proteins. The ligand precursors and complexes are also evaluated for their in vitro antiproliferative activity against ovarian (A2780) and prostate (PC3) human cancer cells and in normal fibroblasts (V79) to check the selectivity of the compounds for cancer cells.

Atomically Defined Nanopropeller Fe3Co6Se8(Ph2PNTol)6: Functional Model for the Electronic Metal-Support Interaction Effect and High Catalytic Activity for Carbodiimide Formation.

Atomically defined interfaces that maximize the density of active sites and harness the electronic metal-support interaction are desirable to facilitate challenging multielectron transformations, but their synthesis remains a considerable challenge. We report the rational synthesis of the atomically defined metal chalcogenide nanopropeller Fe3Co6Se8L6 (L = Ph2PNTol) featuring three Fe edge sites, and its ensuing catalytic activity for carbodiimide formation. The complex interaction between the Fe edges and Co6Se8 support, including the interplay between oxidation state, substrate coordination, and metal-support interaction, is probed in detail using chemical and electrochemical methods, extensive single crystal X-ray diffraction, and electronic absorption and Mössbauer spectroscopy.

Geometric and electronic structure of a crystallographically characterized thiolate-ligated binuclear peroxo-bridged cobalt(III) complex.

In order to shed light on metal-dependent mechanisms for O-O bond cleavage, and its microscopic reverse, we compare herein the electronic and geometric structures of O2-derived binuclear Co(III)- and Mn(III)-peroxo compounds. Binuclear metal peroxo complexes are proposed to form as intermediates during Mn-promoted photosynthetic H2O oxidation, and a Co-containing artificial leaf inspired by nature's photosynthetic H2O oxidation catalyst. Crystallographic characterization of an extremely activated peroxo is made possible by working with substitution-inert, low-spin Co(III). Density functional theory (DFT) calculations show that the frontier orbitals of the Co(III)-peroxo compound differ noticeably from the analogous Mn(III)-peroxo compound. The highest occupied molecular orbital (HOMO) associated with the Co(III)-peroxo is more localized on the peroxo in an antibonding π*(O-O) orbital, whereas the HOMO of the structurally analogous Mn(III)-peroxo is delocalized over both the metal d-orbitals and peroxo π*(O-O) orbital. With low-spin d6 Co(III), filled t2g orbitals prevent π-back-donation from the doubly occupied antibonding π*(O-O) orbital onto the metal ion. This is not the case with high-spin d4 Mn(III), since these orbitals are half-filled. This weakens the peroxo O-O bond of the former relative to the latter.